Fluid pressure operated actuator



5, 1952 F. w. MEREDITH ETAL 2,605,615

FLUID PRESSURE OPERATED ACTUATOR I Filed May 22', 1951 fatented Aug. 5, i952 2,605,615 g I FLUID rnssspnn OPERATED ACTUATOR 1' Frederick WillianrIi/ieredith and David William x Righton, Cricklewood, London, England, as-

' signers to, S. Smith and Sons ited; London, England Application May 22, issijseriai No. 227,566 I In Great Britain May 19, 1950 .6 Claims. (01. 60-437) This invention relates to fluid pressure operated actuators for control surfaces for dirigible objects.

It is the object of the present invention "to provide a novel and simple actuator of the type referred to wherein a main actuator piston and cylinder provide the force acting on the control surface required to meet short period demands and an auxiliary actuator piston and cylinder provide the force required for long period demands.

According to the present invention a fluidpressure operated actuator for control surfaces for dirigible objects comprises a main actuator cylinder, a piston within said cylinder, said piston acting on a control surface through a substantially rigid connection, an auxiliary cylinder, an auxiliary piston within said cylinder, restricted fluid paths connecting corresponding ends of said main and auxiliary cylinders, together with a connection from said auxiliary piston'to said control surface, said auxiliary piston and cylinder and said connection being such that a persistent load on the main piston is relieved by the auxiliary piston. j

The connection and th control surface conveniently comprises a resilient link, the stroke of the auxiliary piston being sufficiently great to ensure that the resilient link can be fully compressed or extended when the main piston isnear the limits of its travel. Y Y

Preferably the cross-section of the auxiliary piston and cylinder is large compared with that of the main piston and cylinder.

The flow of pressure fluid to the main cylinder is most conveniently controlled by a valve and follow-up mechanism of the conventional kind.

It is frequently found that in th control of a dirigible object that the control moments applied thereto can be divided into two classesshort-period low amplitude moments for stabilisation and long-period large amplitude moments for course change. It will be seen that by using an actuator system in accordance with the present invention th short period stabilising moments can be supplied by the main piston and cylinder while the long period large amplitude moments are supplied by the auxiliary piston and cylinder.

A hydraulic actuator for an aircraft elevator, constructed in accordance with the invention, will now be described with reference to the accompanying drawing.

Movement of the elevator, indicated at I, is conbetween the auxiliary piston- (England) Limtrolled by a gyroscope 2 having two precessional degrees of freedom to control the aircraft-"in pitch. v Elevator l is actuated by rotation ofashaft 3 to which it is rigidly attached. There are also attached to the shaft two arms 4 and-5 of equal length. Arm i is connected by means of alin'k 6 to the piston rod 9 of a main actuator piston it, link 6 being'pivoted at 'l' to arm 4 and at 8 to piston rod 9. .Arm 5 is connected through a spring-containing cylinder l land a coil spring l2 carried therein to the piston rod l3 of an auxiliary piston It, the cylinder-Handspring l2 effectively forming a'resilie'nt link pivoted to arm 5 at It and to rod 13 at'lli. Spring 12 is such that when compressed through a distance equal to half the stroke of the main' piston it exerts a moment equal to the; maximumrequired to be ap lied to the elevatori Main piston- [0 moves in a conventional'cylinder lln- Pressure fluid is fed to one side or other of fpis't'on til from an inlet pipe under the -contro1-of-a-valve i8; fluid from the exhaust side of the cylinder being allowed to 'fiow through outlet pipe 31.

v The v position ofvalve I8 is controlled'by a-shaft Auxiliary piston it, of considerably greater area than'piston l0, moves in a conventional cylinder 25 and 'has twicethe stroke of-the main piston. One end of cylinder '25 isconnected," through a pipe 2i provided with a restrictive orifice 23, to one end of cylinder l7 -whne the other end is connected through a pipe 22"'pro-- vided with a restrictive orifice 24 to the other end of cylinder 11. The sense of connection-is such that the moments produced by the two pistons about shaft 3 aid each other.

The position of shaft is, and hence of valve I8, is controlled by means of a floating link 26 one end of which is pivoted to it, as at 21, and normally substantially at right angles to it. The other end of link 26 is provided with a slot 30 egaging with a pin 28 attached to piston rod 9 in the vicinity of its pivot with link 5. Link 28 is pivoted at an intermediate point 29 to one end of a link 36. The other end of link 36 is pivotally connected at 3! to the outer gimbal ring 32 of gyroscope 2. Outer gimbal ring 32 is pivotally mounted, as indicated at 33, relative to the aircraft for rotation about an axis parallel to the aircraft pitch axis. The inner gimbal ring and rotor of the gyroscope are conventionally pitch, valve l8, piston In and piston [4 are in 3 n their mid-positions while spring I2 is unstressed.

Upon the occurrence of deviation of the aircraft from its datum pitch attitude the resultant movement of link 35 will open valve l8 and the resultant motion of piston 10, communicated to floating =link 26 via pin 28 and :slot '30 will tend to close valve f8. It will be seen that if the distance between pivot 21 and pin 28 is a while that between 29 and pin 28 is b the resultant displacement of valve I8 is equal to (displacement of piston rod 9) plus (displacement of link 36). Fluid will flow into cylinder 11 until the displacement of valve I8 is zero, that is to say until (displacement of piston rod 9):

ment of the control surface has been made there is a pressure differenceacross pistonfll, pressure fluid will flow through pipes 2| and 22 via orifices 23 and 2'4 causin movement of the auxiliary piston 14 to-compress or extend the resilient link formed by cylinder H and spring l2 and apply oor-responding moment to the elevato 1 until, if the demand is stationary, th requisite moment is supbliedlargely by the auxiliary piston l4. 7

:By appropriate choiceof the size of orifices 23 and Min relation to the size'of the auxiliarycylinder-25 the time constant of the auxiliary piston and cylinder can be made small compared with long-period demands and large compared with short period demands so that long period demands for course changing Will, efiectively, be met by the auxiliary piston and cylinder I l and 25 while-short period stabilising demands will be metbythe mainpistonand cylinder ,1!) and I7.

7 Weclaim:

A fluid pressure operated actuator for control surfaces for dirigible objects comprising a main actuator cylinder, a piston Within said cylinder, said piston acting on a main control surface through a substantially rigid connection, an auxiliary cylinder, an auxiliary piston within said cylinder, restricted fluid paths connecting corresponding ends of said cylinders, together with means for relieving a persistent load on the main piston,said means being actuated by the auxiliary piston.

2. A fluid pressure operated actuator for control surfaces for dirigible objects comprising a main actuator cylinder, a piston within said cylinder, said piston acting on a main control surface through asubstantially rigid connection, an auxiliary cylinder, an auxiliary piston within said cylinder, restricted fluid paths connecting corresponding ends of said cylinders together with a resilient connection between said auxiliary piston and said control surface, said auxiliary piston and cylinder and said connection being so dimensioned that a persistent load on the main piston is relieved by the auxiliary piston, the stroke of the auxiliary piston being such that the resilient member can be fully compressed or extended when the main piston is near the limits o'f.;its travel.

3. An actuator as claimed in claim 2 wherein the cross-section of the auxiliary piston and cylinder is large compared with that of the main piston and cylinder.

4. An actuator as claimed in claim 3 wherein the resilient link is fully compressed or extended when the auxiliary piston is exerting a control moment on the control surface substantially equal to the maximum required to be exerted thereon.

5. An actuator as claimed in claim 4 comprising also a valve and follow-up mechanism to control the flow of pressure fluid to the main cylinder.

'6. Afluid pressure opera-ted actuator for-control surfaces'for dirigible objects comprising a main actuator cylindena piston within said cylinder, said piston acting on a main controlsurf'ace througha substantially rigid connection, .an auxiliary cylinder, an auxiliary piston within said cylinder, said auxiliary piston and cylinder having'a large cross-section compared with that or the main piston and cylinder, restricted fluid paths connecting corresponding ends of said 'main and auxiliary cylinders, together with means adapted to relieve a persistent load on the main piston, said means being .actuated by the .au'xiliary piston.

' FREDERICK WILLIAM MEREDITH.

DAVID WILLIAM RIGI-ITON.

No references cited. 

